Efficiency & Improving a Design — Drills · Grade 8 Science
Chapter: Work & MachinesWhat these drills covers
By the end of Efficiency & Improving a Design you should be able to:
- I can calculate efficiency using useful output energy and input energy.
- I can evaluate a design improvement using measurements and a stated criterion.
6 questions, numeric, written answer and multiple choice, each with a worked explanation.
Vocabulary used: efficiency, criterion, energy dissipation, model, evidence, system boundary, assumption.
Problem 1
Answer and explanation
60 %
300 ÷ 500 × 100 = 60.
Problem 2
Answer and explanation
Use the same load and lifting height, with comparable speed and measurement methods.
Problem 3
Answer and explanation
75 %
300/400 × 100 = 75 percent.
Problem 4
Answer and explanation
300 J
0.60 × 500 = 300 J.
Problem 5
- energy is destroyed
- some energy is always transferred to the surroundings, mostly as heat
- machines are badly made
- energy cannot be measured
Answer and explanation
some energy is always transferred to the surroundings, mostly as heat
Friction and resistance always disperse some energy.
Problem 6
Answer and explanation
Lubricating moving parts reduces friction, so less energy is transferred to heat as surfaces slide. Reducing unnecessary mass in the moving parts means less energy goes into accelerating the machine itself rather than the load. Both reduce the wasted branch of the energy transfer, leaving more of the input to do the intended job.
Response criteria
- State a scientifically accurate conclusion.
- Show the data, mechanism, or calculation that supports it.
- Include units, conditions, or limits where relevant.